It is often necessary to provide a connector with coiled tubing. This need occurs when a downhole tool needs to be attached to the end of a string of coiled tubing. It also occurs when the amount of coiled tubing required to perform the service cannot be contained on a single reel as one continuous length of pipe. This could be a result of lift capacity of handling equipment or the volume capacity of the work reel. Additional examples of oilfield circumstances that require a connector include situations such as repairing a leak or a damaged area in an existing continuous length of coiled tubing or retrieving a length of coiled tubing (such as a velocity string) from a well.
One method of connecting a connector to coiled tubing is by deforming the coiled tubing into preformed pockets on the outside diameter of the connector. By connecting the connector to the coiled tubing with this method, a strong secure connection is made that can resist both tensile loads and torsion loads. A connector that can be used for this application needs to provide tensile strength similar to the strength of the coiled tubing. In the case of a spoolable connector, the connector is also required to bend around the coiled tubing reel and the injector gooseneck during operation. This bending and straightening sequence causes low cycle fatigue in the coiled tubing and the connector.
Problems that occur when using dimples to connect coiled tubing to a connector include, but are not limited to, evaluating tensile strength of the connection and providing a solid connection that does not restrict bending of the coil around the reel or gooseneck when two sections of coiled tubing are connected together. For connectors attached to the end of a string of coiled tubing a pull test can be conducted on the connector with the injector. This validates the integrity of the connector for the applied load, but material often yields and could compromise the connection. This test does not determine the pull apart limit of the connection. When two sections of coiled tubing are connected together using dimples it is not possible to perform a pull test that validates the strength of the connection.
Currently the size and depth of the dimple is not controlled. Dimples are commonly formed by using a hydraulic ram that presses a pin with a spherical end into the surface of the coiled tubing, yielding the coiled tubing material into a preformed dimple on the connector OD. The force used to make the dimple is controlled by adjusting the hydraulic pressure applied to the ram. This pressure is commonly set high enough to insure that all tubing strengths and thicknesses can be fully dimpled with a set force per pin. Since coiled tubing is supplied in various yield strengths and wall thicknesses, the amount of deformation and yielding can vary when dimpled with a standard force per pin. Testing has shown that dimples that are too shallow or too deep result in a connection that can fail from tensile loads and bending loads significantly before connections that are made with the preferred dimple depth. Therefore, it is important to know if a dimple has been properly formed.
If the preformed dimple in the connector body is slightly larger than the dimpling pin, then the dimple will sufficiently fill the cavity to make a secure connection. If all of the dimples in the coiled tubing fit snuggly in the preformed pockets of the connector, then a tensile load is not carried uniformly, overstressing some of the dimples as shown in FIG. 1. FIG. 1 illustrates a prior art connector-coiled tubing connection wherein some of the dimples are overstressed. Connector 12 is connected to coiled tubing 14 via dimples 18 formed in coiled tubing 14 and mated with pockets 16 (see FIG. 2) preformed in connector 12. Coiled tubing 14 is overstressed proximate dimples 18 at the shaded regions 20.
Another drawback of the prior art dimple connections is illustrated in FIG. 2. When the preformed pocket 16 in connector 12 is significantly larger in radius and volume, as shown in FIG. 2, then its respective dimple 18 does not completely fill the pocket cavity 22 and the connection is loose, allowing connector 12 to move slightly relative to coiled tubing 14. This produces a gap 24 between the connector shoulder 26 and coiled tubing 14. Gap 24 can cause problems when the connector assembly passes through the coiled tubing stripper. For a conventional spoolable connector, both of these conditions, overstressed and gap, can cause problems leading to reduced performance.
Therefore, there is a desire to provide an improved dimple connection for coiled tubing and method of providing coiled tubing dimple connection integrity that addresses drawbacks of the prior art systems and methods. There is a further desire to provide a method of validating the strength of a connection while allowing flexibility in the connection to enhance low cycle fatigue performance during bending. There is a still further desire to provide a secondary barrier without compromising the performance of the primary seal.